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Turbulence for natural external convection

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Old   April 17, 2024, 07:55
Default Turbulence for natural external convection
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Gustavo
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Hello. I'm trying to set up a case of natural external convection where a fluid flows around a hot cylinder due only to temperature differences. I have done laminar tests and it worked fine with great results.

Now I wanna add turbulence (by modifying Rayleigh parameters) but I can't figure out how to set up the initial BCs for turbulence.

My professor told me to use k-omega-SST model, but I'm not able to judge the best BCs for the files of k/omega/alphat/nut.

In my case the fluid is initially quiescent (zero velocity) and starts moving only due to the natural convection, but because of this I can't calculate what the initial values for k/omega should be, since the fluid isn't moving at the beggining.

Also, my mesh consists of:

inlet/outlet = patches
superiorPlane/inferiorPlane = symmetryPlane
cylinderWall = wall
frontAndBack = empty

I'm a begginer at OpenFOAM, so I'm sorry for stupid mistakes.


No fvModels present
No fvConstraints present
#0 Foam::error:rintStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/lib/x86_64-linux-gnu/libc.so.6"
#3 Foam::divide(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) at ??:?
#4 Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam:perator/<Foam::fvPatchField, Foam::volMesh>(Foam::tmp<Foam::GeometricField<doub le, Foam::fvPatchField, Foam::volMesh> > const&, Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > const&) at ??:?
#5 Foam::fluidThermo::nu() const at ??:?
#6 Foam::RASModel<Foam::compressibleMomentumTransport Model>::nu() const at ??:?
#7 Foam::kOmegaSST<Foam::eddyViscosity<Foam::RASModel <Foam::compressibleMomentumTransportModel> >, Foam::compressibleMomentumTransportModel>::F2() const at ??:?
#8 Foam::kOmegaSST<Foam::eddyViscosity<Foam::RASModel <Foam::compressibleMomentumTransportModel> >, Foam::compressibleMomentumTransportModel>::F23() const at ??:?
#9 Foam::kOmegaSST<Foam::eddyViscosity<Foam::RASModel <Foam::compressibleMomentumTransportModel> >, Foam::compressibleMomentumTransportModel>::correct Nut() at ??:?
#10 ? in "/home/workstation1/OpenFOAM-10/OpenFOAM-10/platforms/linux64GccDPInt32Opt/bin/buoyantFoam"
#11 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#12 ? in "/home/workstation1/OpenFOAM-10/OpenFOAM-10/platforms/linux64GccDPInt32Opt/bin/buoyantFoam"
Floating point exception (core dumped)
Attached Files
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File Type: zip system.zip (2.9 KB, 0 views)
File Type: zip constant.zip (2.3 KB, 0 views)

Last edited by gushrqcosta; April 17, 2024 at 10:01.
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Old   April 17, 2024, 10:40
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Hey,


It looks like a division by 0 occured somewhere!


Try to avoir 0 values in your turbulent boundary conditions (you can use 1e-8 for instance) and in your fluid properties.


Concerning initial values for turbulence, I guess you could estimate the max velocity reached once your convective pattern is established (a few m/s?) and get approximative values for k and omega. Initial values are just that, for the initial steps of the simulation. The turbulent quantities should converge towards realistic values afterwars.
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